A filling valve fills liquid from a filling machine vessel into containers. When the filling valve is opened a complete pressure equalization takes place between the vessel and the container to be filled. The container is held in the filling position by a vertically movable centering member. At the end of the filling operation, with the centering member still holding the container, a return gas tube extending into the container can be emptied and the volume of the container above the liquid level can be relieved without any inflow of atmospheric air. Further, the usual expansion below the liquid level is avoided. The centering member along with the filling valve can be lowered into the filling position by a cam disc and a pressure spring and/or assisted by the overpressure within the filling machine vessel. After movement by the cam disc the centering member and filling valve can be pressed against the container opening by the pressure spring and/or the pressure in the vessel. An upwardly extending piston member forming part of the piston-cylinder unit contains the return gas tube and can move independently of the return gas tube for placing the filling valve in the open condition with complete pressure equalization by cooperation with a double lever arm arrangement. When the filling liquid within the container reaches the lower end of the return gas tube, the piston member is lifted by the cam disc and simultaneously there is an increased volume communicating with the container while the centering member is still pressed on the container with the return gas tube being emptied and with the return gas connection to the vessel being cut off whereby the increased volume is exposed to atmospheric pressure.